Linear viscoelasticity in incompatible polymer blends in the melt in relation with interfacial properties
Résumé
A quite general characteristic of the theology of incompatible polymer blends in the melt is their highly elastic behavior at low frequencies, corresponding to long-time relaxation processes. For emulsions of Newtonian liquids, this property can be readily connected to interfacial tension α: in a macroscopic flow, suspended droplets of radius R are subjected on the one hand to a viscous drag related to the viscosity μm of the matrix liquid and tending to deform their shape, and on the other hand to and elastic force of the order of α/R opposing the deformation. From a rheological point of view, the emulsion shows viscoelastic behavior with characteristic relaxation times of the order of μmR/α. Blends of incompatible uncrosslinked polymers in the molten state can also be considered as emulsions, but the behavior of the phases becomes viscoelastic by itself. A recent model, which accounts for the viscoelasticity of the phases, the polydispersity in size of the droplets and their hydrodynamic interactions, allowed us to explain the linear viscoelasticity of some selected polymer blends.